Implementing trial period [duplicate]

This question already 开发者_开发知识库has answers here: Closed 11 years ago.

Possible Duplicate:

how can i make my product as a trial version for 30 days?

I would like to implement a trial period for my application.

What would be the best way of doing this?

I thought of writing the start date of the trial period to the registry.

But my guess is that would be just to easy to overcome by for example using CCleaner.

What would be a better way of doing it?

PS

I'm not looking for a 100% watertight solution, since that just isn't possible.

EDIT

I'm not looking for an online solution.

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I would try to store as little as possible on the client pc and use a web service distributed solution.

Still hackable of course but at least there is nothing to find or edit on the client and you have control from your server on who starts the application.

Of course this assumes the client pc should be online for the application to work.

surely improvable but as you say there is no perfect solution.